The young boy, Gustav Larson is interested in Dragon Training and even pretends to ride a dragon with a sheep and plays secretly in the Academy while the Riders are away. However, he accidentally burns one of the crates and panics to what he would do as the flame grows bigger. Luckily, the Riders arrive and stop the fire. Hiccup told him he can't play in the Academy, Gustav says he isn't playing but dragon training and wants to be a Dragon Rider. Snotlout tells Gustav all the positions are taken so unless one of them 'kicks the bucket' he's not able to join.
Ironically it's Snotlout who's going to kick the bucket. He is now convinced he is about to die after seeing three of the five sign posts of Valhalla that takes great warriors into an eternal paradise. The Riders try to tell Snotlout the sign posts of Valhalla is nothing but an old wives' tale but Snotlout seemingly witnesses the three out of five sign posts and is unconvinced. Fishlegs and Astrid justify Hiccup's opinion but fail, so before Snotlout dies he picks Gustav as his replacement, Hiccup doesn't agree with this and tells Snotlout he only saw three and there's still two more, but the fourth sign post: The Bird of Death, is witnessed by Snotlout making him more convinced his death comes. Hiccup reluctantly allows Snotlout to train Gustav and head out for a scouting mission on Outcast Island.
From there, unable to get a closer look, they barely see the Outcasts and Beserkers building something huge and the Twins' suggests they blow it up right away. Hiccup denies their suggestion, and tells everyone to just look for more signs they could now engage. Back at Dragon Academy, Snotlout trains Gustav, and the Riders watch later on. Every time Snotlout trains something to Gustav he gets painfully burned, hit or eaten. Hours later, Snotlout vested and blesses Gustav he is now ready to replace him and takes his place with Hookfang. Snotlout has gone far, and Hiccup tells him first he isn't really dying, second no one vested him with any power, and lastly Gustav isn't ready to be a Dragon Rider as there is way more training than just feeding it and getting on its back, which both of it is neither accomplished greatly by Gustav. Snotlout tries to justify Gustav is ready and wishes his final farewell to the Riders especially Astrid. As Hiccup tells him for the last time, he's not dying. The fifth sign post is witnessed by Snotlout: The Shepard's curse, that involves a flock of sheep following him. Snotlout panics and seemingly dies and is sent to Valhalla. Actually, Snotlout fainted and is still alive but still convinced he is about to die and tries to convince Hiccup to let Gustav take his place. Hiccup still doesn't agree and the Riders tell him the only way that a person can be a Dragon Rider is to have experience, and the dragon needs experience too. Gustav seemingly quit and leaves, and Snotlout continues with his backup plan by burying Hookfang and him and the Twins' begin digging a hole in the academy. Deep in the forests, Gustav is actually finding a dragon that suits him, after encountering and denying a couple of Terrible Terrors and a Deadly Nadder, he wants to train a wild young Monstrous Nightmare, after recalling what Snotlout said about this dragon. Gustav is confident and attempts to train the dragon but his first attempt fails. Just as it seems that the dragon is about to kill Gustav, he smells food inside his satchel. Using basic training, Gustav uses the fish to bond with the dragon, but this second attempt somehow fails after he throws the food at the dragon's face. Furious, the dragon chases Gustav and tries to eat him.
Back at the Academy, the Riders plan for a diversion on Outcast Island but gets interrupted when a young Monstrous Nightmare jumps in inside the Academy, which has now bonded a bit by Gustav. Gustav names and introduces his Monstrous Nightmare: Fanghook. Snotlout is angry after hearing that. Gustav wants to prove to the Riders that he is ready and while they try to prove it, Fishlegs come up with a plan by pretending Gustav is a pretty good replacement for Snotlout and finally make him convinced that he is not dying, Hiccup and Astrid quickly agrees. Hiccup gives him a few obstacle courses which he really does it bad, but they pretend that he has done well. Snotlout grows angry and is seem to regret his last wishes of him being replaced by Gustav, that he is better than Snotlout. The Riders are pretending to appreciate Gustav even more than Snotlout. But Snotlout discovers their plan, that they're actually trying to convince him that his not dying. While Hiccup is talking to Snotlout he notices that Snotlout has been scratching his butt all day, and Snotlout tells him that he filled his pants with broad grass, as the Twins told him it prevents saddle chaffing. Hiccup suspects the Twins have been messing with Snotlout all along, but Ruff and Tuff say that they didn't do anything, but their plan is blown as chickens are dropped in their hands, that are actually coming from Barf and Belch and they flee to avoid trouble. Hiccup and Astrid tells Snotlout that he still hasn't figured out, that he is not dying and the twins were actually messing with him, Snotlout is glad to hear that. For Gustav though, he and his dragon gets kicked out by of the academy by Snotlout and he chases the Twins' in anger. Stoick comes in and informs Hiccup that Trader Johann overheard Dagur and the Berserkers that they are about to test fire some kind of new weapon, Hiccup suspects its what they saw earlier.
Hiccup assembles a couple of Riders on a scout mission on Outcast Island, Stoick tells them not to engage, Gustav overhears their conversation and plans to engage the enemy themselves in order for them to be joined in the academy. Later that night, Astrid distracts the Berserkers in order for Hiccup and Snotlout to get a closer look at this new weapon. Unbeknownst to them they actually heading for a trap that Dagur planned all along. As soon as the ambush is in motion, Gustav emerges and Dagur is shocked to see another Rider, the Outcasts and Beserkers fire their weapon and traps Gustav. But Dagur orders them to save the ammunition for Hiccup. Gustav gets in trouble as Berserkers and Outcasts closes in, Hiccup tells him to move by using his battle cry to reinforce Fanghook to flame up his body. Gustav panics and quickly flees from the battlefield.
Hiccup is locked on target for the weapon and is shot and captured and crashes down near enemy lines. Snotlout tries to make Gustav help Hiccup and Toothless, but he is too scared and thinks that he can't do it. Snotlout tries to inspire and boost his spirits by telling him that he's riding a Monstrous Nightmare and recalling what he said about this dragon, with only minutes left before Hiccup and Toothless meet their doom, Gustav finally agrees and joins Snotlout on their attack against the Berserkers. Hiccup manage to gets free. And all 3 of them destroys Dagur's weapon and head home for Berk, Hiccup is proud and congratulates the two. Dagur wonders what went wrong, Salvage tells Dagur it may have been the execution, Dagur mistakenly thinks execution means chopping off someone's heads, the Berserkers and Outcasts slowly walk away and panic.
Hiccup informs Stoick that Dagur intentionally leaked the information to Trader Johann, who in turn would give the information to Berk and lure the Riders to the Outcasts. Stoick is just glad that they all return safely to Berk. Gustav is upset that he is certain that due to his actions his not ready to join the academy. To cheer him up, Hiccup tells Gustav that he will be the Academy's very first Junior Apprentice Auxillary Reserved- Backup Replacement Rider in Training (4th Class). Gustav is happy to hear that, but Hiccup tells him that he has to study, clean out the Dragon Stalls, and no more unauthorized dragon flying meaning that he has to let Fanghook go because both of them are not ready, Gustav sadly understands. Hiccup and Snotlout join Gustav in the forest, the place where the two meet, where he is about to let Fanghook have his freedom but Fanghook wants to stay with his Rider, Gustav sadly tells him to go and Fanghook walks away. Hiccup tells him that it was the right thing to do even though it was hard form him to let Fanghook go, while Snotlout brags that nothing can replace him. Gustav decides to stay in the forest for some alone time to think, the moment Hiccup and Snotlout leaves. Gustav is revealed to have set them up and calls Fanghook for the clear. As they secretly train in private in the forest, the two happily decide they want to train together as Fanghook joyfully bites and carries Gustav while he laughs.
- Jay Baruchel as Hiccup
- America Ferrera as Astrid Hofferson
- Christopher Mintz-Plasse as Fishlegs Ingerman
- T.J. Miller as Tuffnut Thorston
- David Faustino as Dagur the Deranged
- Lucas Grabeel as Gustav Larson
- Nolan North as Stoick the Vast
- Zack Pearlman as Snotlout Jorgenson
- Paul Rugg as Savage
- Andree Vermeulen as Ruffnut Thorston
- Toothless - Night Fury (Hiccup's Dragon)
- Stormfly - Deadly Nadder (Astrid's Dragon)
- Meatlug - Gronckle (Fishlegs's Dragon)
- Hookfang - Monstrous Nightmare (Snotlout's Dragon)
- Barf and Belch - Hideous Zippleback (Ruffnut and Tuffnut's Dragon)
- Gustav will be receiving his own dragon named Fanghook, named after Hookfang.
- This is the second episode where a non-teen Viking on Berk recieves a dragon, in this case, Gustav Larson. The first time is in How to Pick Your Dragon when Stoick the Vast receives Thornado.
- Fanghook has a similar colour configuiration as the monstrous nightmare as the one Astrid trained when she was on Outcast Island diguised as Heather.
- The Deadly Nadder that Gustav spotted also has a similar colour configuration as the one that Hiccup and Mildew trained also on Outcast Island in We Are Family Part II. It is preceded by A View to a Skrill Part 2 and is succeeded by Free Scauldy.
- The Beserkers and Outcasts appear to have combined their crests. There weapon had large round symbol with a Skrill, like the Beserker crest, and has large spikes around it, like the Outcasts' shields.
- the five sign posts of Valhalla are as follows:
- 1:flying fish (salmon spawning)
- weeping rocks (wet rocks on the beach)
- singing tree's (gust of wind)
- bird of death (dead chicken)
- the shephards curse (sheep attracted to broad grass in Snotlout's pants)